# X90CP154.32.S1 PWM current measurement and control

**URL:** <https://community.br-automation.com/t/x90cp154-32-s1-pwm-current-measurement-and-control/11851>\
**Category:** Mechatronics & Motion\
**Tags:** x20, plc\
**Created:** [July 7, 2026, 6:42am UTC](https://community.br-automation.com/t/x90cp154-32-s1-pwm-current-measurement-and-control/11851 "2026-07-07T06:42:57Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![Saeed\_Rostami](https://avatars.discourse-cdn.com/v4/letter/s/FF8800/32.png) [@Saeed\_Rostami](https://community.br-automation.com/u/Saeed_Rostami)\
**Post date:** [July 7, 2026, 6:42am UTC](https://community.br-automation.com/t/x90cp154-32-s1-pwm-current-measurement-and-control/11851/1 "2026-07-07T06:42:57Z")

</div>

Hi, I have a X90CP154 in my project. I need to control the current in the PWM output port. Now I read the current from the channel and there is a huge difference. The ammeter shows 600 mA, but the port number after multiplying by 305 comes to 720 mA. Why is there this difference? The settings are in the following figures

 ![Screenshot 2026-07-07 084227](https://europe1.discourse-cdn.com/brcommunity/original/2X/4/4863af4b7a311913eb6832fa216e7494d5df8be7.png)

 ![image (1)](https://europe1.discourse-cdn.com/brcommunity/original/2X/c/cf58fe2270a4f91fd3ce3a8f5a7b8e57a2bf8ee8.png)

 ![image](https://europe1.discourse-cdn.com/brcommunity/original/2X/2/26fb5f7067d25ce120a511fe9985d74305db2704.png)

---

<div class="post-metadata">

**Author:** ![christoph.hilchenbac](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/christoph.hilchenbac/32/423_2.png) [@christoph.hilchenbac](https://community.br-automation.com/u/christoph.hilchenbac)\
**Post date:** [July 7, 2026, 2:23pm UTC](https://community.br-automation.com/t/x90cp154-32-s1-pwm-current-measurement-and-control/11851/2 "2026-07-07T14:23:09Z")

</div>

Hi,

Measuring current at a PWM output isn’t exactly easy.  
You really need a good TrueRMS meter for that.  
Alternatively, an oscilloscope with a shunt resistor could be very helpful for checking this.

A followed up question is what is configured here: [Current measurement configuration](https://help.br-automation.com/#/en/4/hardware%2Fx90cp154.xx-s1%2Fx90cp154_sw%2Fkonfiguration_strommessung.html)

 ![image](https://europe1.discourse-cdn.com/brcommunity/original/2X/3/3161abca13666bbee50155ce166d6e63b4a55549.png)

---

<div class="post-metadata">

**Author:** ![ChristianBauer](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/christianbauer/32/14073_2.png) [@ChristianBauer](https://community.br-automation.com/u/ChristianBauer)\
**Post date:** [July 8, 2026, 7:49am UTC](https://community.br-automation.com/t/x90cp154-32-s1-pwm-current-measurement-and-control/11851/3 "2026-07-08T07:49:00Z")

</div>

Hi Saeed,

according to the technical data, the error is based on the range of 20 A! As 1 % is 200 mA an overall error of 120 mA is within spec. But usually the error is much lower.

Some tips:

- Most meters (as e.g. the Flukes) are measuring RMS only in AC mode, but PWM is NOT AC, as the signal is always positiv to GND. Set the measure mode to “arithmetic” and the value should be more accureate.
- The Measuring period must be a multiply of the PWM period, otherwise you would not capture a full period.
- I suggest to not use the Frequency from I/O datapoint but set it to “fixed”. Then you can select the current measurement as synchronous to PWM period.

One question: What do you mean with “secondary input” ?

Kind regards,

Christian

---

<div class="post-metadata">

**Author:** ![Saeed\_Rostami](https://avatars.discourse-cdn.com/v4/letter/s/FF8800/32.png) [@Saeed\_Rostami](https://community.br-automation.com/u/Saeed_Rostami)\
**Post date:** [July 9, 2026, 7:58am UTC](https://community.br-automation.com/t/x90cp154-32-s1-pwm-current-measurement-and-control/11851/4 "2026-07-09T07:58:22Z")

</div>

Hi Christian

thanks for your sharing.

it was misspelling.

Regards

---

<div class="post-metadata">

**Author:** ![Saeed\_Rostami](https://avatars.discourse-cdn.com/v4/letter/s/FF8800/32.png) [@Saeed\_Rostami](https://community.br-automation.com/u/Saeed_Rostami)\
**Post date:** [July 9, 2026, 8:05am UTC](https://community.br-automation.com/t/x90cp154-32-s1-pwm-current-measurement-and-control/11851/5 "2026-07-09T08:05:32Z")

</div>

Hi everyone!

Thanks for your time and attention.

I changed RMS to arithmetic and now it is fine!

Now both measurements are equals.

Regards